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Desde o clássico experimento de Miller em 1953 evidenciando a formação de aminoácidos em condições de Terra primitiva, a química do período pré-biótico ainda é muito discutida. Cita-se, por exemplo, o papel da teoria sulfociânica, que descreve a origem de moléculas orgânicas a partir de compostos contendo enxofre, como o tiocianato de amônio (NH4SCN). Neste contexto, essa Tese aborda um estudo sobre a investigação do NH4SCN em condições pré-bióticas. Para isso, experimentos de oxidação eletroquímica e de irradiação ultravioleta (UV) em amostras contendo NH4SCN em diferentes condições experimentais foram conduzidos. Por eletroquímica acoplada à espectroscopia vibracional no infravermelho (FTIR in situ), identificou-se como o primeiro produto da oxidação do NH4SCN, o dímero tiocianogênio (SCN)2, que é um reconhecido precursor dos oligômeros do período pré-biótico. Em contrapartida, a irradiação UV do NH4SCN levou a formação de enxofre ortorrômbico (S8) e das bases nitrogenadas 4-(3H)-pirimidinona, citosina, purina e adenina, além de outras moléculas. Provavelmente, o cianeto de hidrogênio (HCN) é um dos precursores das biomoléculas supracitadas, contrariando uma possível rota via (SCN)2. Os resultados desse estudo também reforçam a hipótese de que não há formação direta de aminoácidos por irradiação do NH4SCN. Desta forma, propõe-se aqui que a formação dos blocos do DNA, as bases nitrogenadas, também possa ser inserida no contexto da teoria sulfociânica. / Since the classic Miller experiment in 1953 evidencing the amino acids formation under early Earth conditions, the chemistry of the prebiotic period is still very discussed. It is cited, for example, the role of sulfocyanic theory, which describes the origin of organic molecules from sulfur-containing compounds such as ammonium thiocyanate (NH4SCN). In this context, this thesis shows a study about the investigation of NH4SCN in prebiotic conditions. Thereby, experiments of electrochemical oxidation and ultraviolet (UV) irradiation were carried out with samples containing NH4SCN in different experimental conditions. By using electrochemistry coupled to Fourier transform infrared spectroscopy (FTIR in situ), the dimer thiocyanogen (SCN)2 was identified as the first oxidation product of NH4SCN, which is a recognized precursor of the oligomers from prebiotic period. In counterpart, UV irradiation of the NH4SCN led to the formation of orthorhombic sulfur (S8) and the nitrogenous bases 4-(3H)-pyrimidinone, cytosine, adenine and purine, besides other molecules. Probably, hydrogen cyanide (HCN) is one of the precursors of the biomolecules abovementioned, contradicting a possible route via (SCN)2. The results of this study also reinforce the hypothesis that there is no direct formation of amino acids by irradiation of NH4SCN. Thus, it is proposed here that the formation of DNA blocks, the nitrogenous bases, can also be inserted in the context of sulfocyanic theory.

Desde o clássico experimento de Miller em 1953 evidenciando a formação de aminoácidos em condições de Terra primitiva, a química do período pré-biótico ainda é muito discutida. Cita-se, por exemplo, o papel da teoria sulfociânica, que descreve a origem de moléculas orgânicas a partir de compostos contendo enxofre, como o tiocianato de amônio (NH4SCN). Neste contexto, essa Tese aborda um estudo sobre a investigação do NH4SCN em condições pré-bióticas. Para isso, experimentos de oxidação eletroquímica e de irradiação ultravioleta (UV) em amostras contendo NH4SCN em diferentes condições experimentais foram conduzidos. Por eletroquímica acoplada à espectroscopia vibracional no infravermelho (FTIR in situ), identificou-se como o primeiro produto da oxidação do NH4SCN, o dímero tiocianogênio (SCN)2, que é um reconhecido precursor dos oligômeros do período pré-biótico. Em contrapartida, a irradiação UV do NH4SCN levou a formação de enxofre ortorrômbico (S8) e das bases nitrogenadas 4-(3H)-pirimidinona, citosina, purina e adenina, além de outras moléculas. Provavelmente, o cianeto de hidrogênio (HCN) é um dos precursores das biomoléculas supracitadas, contrariando uma possível rota via (SCN)2. Os resultados desse estudo também reforçam a hipótese de que não há formação direta de aminoácidos por irradiação do NH4SCN. Desta forma, propõe-se aqui que a formação dos blocos do DNA, as bases nitrogenadas, também possa ser inserida no contexto da teoria sulfociânica. / Since the classic Miller experiment in 1953 evidencing the amino acids formation under early Earth conditions, the chemistry of the prebiotic period is still very discussed. It is cited, for example, the role of sulfocyanic theory, which describes the origin of organic molecules from sulfur-containing compounds such as ammonium thiocyanate (NH4SCN). In this context, this thesis shows a study about the investigation of NH4SCN in prebiotic conditions. Thereby, experiments of electrochemical oxidation and ultraviolet (UV) irradiation were carried out with samples containing NH4SCN in different experimental conditions. By using electrochemistry coupled to Fourier transform infrared spectroscopy (FTIR in situ), the dimer thiocyanogen (SCN)2 was identified as the first oxidation product of NH4SCN, which is a recognized precursor of the oligomers from prebiotic period. In counterpart, UV irradiation of the NH4SCN led to the formation of orthorhombic sulfur (S8) and the nitrogenous bases 4-(3H)-pyrimidinone, cytosine, adenine and purine, besides other molecules. Probably, hydrogen cyanide (HCN) is one of the precursors of the biomolecules abovementioned, contradicting a possible route via (SCN)2. The results of this study also reinforce the hypothesis that there is no direct formation of amino acids by irradiation of NH4SCN. Thus, it is proposed here that the formation of DNA blocks, the nitrogenous bases, can also be inserted in the context of sulfocyanic theory.

Cardiovascular diseases (CVD) remain one of the leading causes of deaths worldwide. The formation and presence of aneurysm is a very important question in the study of this CVDs. An aneurysm is a balloon-like bulge on a blood vessel which forms over time. An aneurysm is usually considered to be a result of weakening of the blood vessel walls, this definition has stood over many years without being conclusively proven. Eventually, the aneurysm could clot or burst due to degradation of the aneurysm wall and accumulation of blood. The latter would lead to internal bleeding and result in a stroke. Local hemodynamics have been found to be very important in the study of the evolution of an aneurysm. In this study, a steady flow experimental investigation was conducted using planar Particle Image Velocimetery (PIV) on a rigid flow phantom of an idealised geometry consisting of a curve parent artery and a spherical aneurysm located on the outer convex side of the curvature. The flow phantom was fabricated directly using a commercially available desktop Stereolithography (STL) 3D printer instead of the more conventional investment casting method using a core. Although 3D printing technologies have been around for many years, the fabrication of flow phantoms by direct printing is still largely under-explored. This thesis details the results of investigation into the optimal printing and post-printing procedures required to produce a flow phantom of suitable clarity and transparency. Other important areas of concern such as the geometric accuracy, surface topography and refractive index of the final model are also investigated. A planar PIV is conducted to study the impact of flow rates on the local flow field in and around the aneurysm and their impact on the wall shear stress. It was found that direct 3D printing is appropriate for the fabrication of flow phantoms suitable for PIV or other flow visualisation techniques. It reduces the complexities and time needed compared to the conventional investment casting methods. It was observed that the optical properties of the printed material such as the high refractive index (RI) and the transmittivity of light could cause a problem in large models. From the PIV measurements it was found that flow rates affect the flow field in both the parent artery and the aneurysm. First, high velocities were observed on the outer curvature of the parent artery. Secondly the centre of rotation in the aneurysm is not at the geometric centre but is displaced slightly in the direction of the flow. Finally, the flow rate affects the angle in which flow enters the aneurysm from the parent vessel. This change in the flow angle affects the flow within the aneurysm. A higher flow rate in the parent artery increases the incident angle which brings the centre of rotation closer to the geometric centre of the aneurysm, this changes the location and magnitude of high velocities and hence the local wall shear stress (WSS) on the wall of the aneurysm. This may have implications in the evolution of aneurysms. / Mechanical and Industrial Engineering